Should I shut my phone off before replacing the battery?

Zoe,

When doing ANY phone repair always power off the device first before tearing into it. After you tear into your device the first thing you always do is disconnect the battery cable to reduce the risk of possibly shorting anything out during a repair. The percentage of the battery does not matter when you’re going to take it out of the device. The only thing that matters is you properly charge the phone to 100% after installation.